Gas supplies are being returned to essential services, including hospitals, and to most of the upper North Island dairy processing factories which have been forced to suspend operations after the first break in the Maui gas pipeline in 30 years.

As coordinator of the gas emergency, Auckland-based network operator Vector said the company was working methodically to excavate at the site of the pipeline break, at a site north of New Plymouth, near White Cliffs.

The work was “methodical” and proceeding in 300 millimetre increments to ensure the safety of workers at the site, and to prevent any further damage to the pipe.

The cause of the weld break is unknown at this stage. Replacement pipe is already at the site, ready for installation once the pipe is exposed.

The return of supply to affected customers is unlikely to be immediate, as systems need to be repressurised where they have been bled of gas that was in the pipe before yesterday’s “curtailment” notice to all gas users other than households.

Fonterra had earlier warned it would be forced to spill some 30 million litres of milk a day during the outage, after closing 15 of its 17 processing facilities in the upper North Island, at a direct cost to the industry of around $20 million a day.

The Environmental Defence Society called on farmers to take care in the way they dump milk on their properties.

"Following on from the Rena disaster with its impact on our marine environment, we now have another major impact, this time on our sensitive freshwater environment,” said EDS chairman Gary Taylor. "Milk in waterways reduces oxygen and kills native and other fauna.

"It seems that every time something fails, it's the environment that suffers.

"We appreciate that most dairy farmers have modern effluent disposal systems and should be able to manage spray disposal to pasture without direct discharge to streams. Any direct discharge or even discharge via effluent treatment ponds to streams is likely to be unlawful.

Taylor said the incident showed New Zealand’s essential infrastructure needed to be more resilient if environmental damage was to be avoided.”

Meanwhile, Acting Energy Minister Hekia Parata has stationed herself at the heart of the emergency response, signalling the government is determined not to look disconnected from the incident in the way that occurred immediately after the grounding of the container ship Rena off Tauranga three weeks ago.